Thermal stability of the Al/PdxW100−x/Si contact systems

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Abstract
Interactions of thin films of Al and Pd‐W alloys (Pd80W20 and Pd20W80) deposited on Si and on SiO2 have been studied using Auger‐electron spectroscopy, Rutherford backscattering spectrometry, x‐ray diffraction, and forward current‐voltage measurements of Schottky‐barrier height. For the bilayer films deposited on the inert substrate of SiO2, Pd reacts with Al, forming Al‐rich Al‐Pd intermetallic compounds at 400 °C. Furthermore, in the Pd‐rich alloys (Pd80W20) Al permeates through the whole alloy film readily at 500 °C, while in the W‐rich Pd20W80 the integrity of the alloy film is preserved even following annealing at 600 °C. For the bilayer films deposited on single‐crystal Si, the results of annealing show extraction of Pd to both sides of the alloy, forming Pd2Si at the Si side and Al‐Pd intermetallic compounds at the Al side. In the case of the Pd‐rich alloy (Al/Pd80W20/Si) contact deterioration due to Al penetration to the substrate interface is observed at 500 °C and possibly at 400 °C. In the case of the W‐rich alloy (Al/Pd20W80/Si) the stability of the contact is preserved even following annealing at 550 °C for 30 min; the structure after the annealing is Al‐Pd/Pd‐W/Pd2Si/Si. The W‐rich alloy is very promising for contact applications in Si devices due to the fact that both a shallow silicide contact and a built‐in diffusion barrier are simultaneously obtained.

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